1. Field of the Invention
The present invention relates to a traffic control apparatus and traffic control method used in an exchange.
In communication services performed via an exchange, for example, asynchronous transfer mode (ATM) communication services performed via ATM exchanges, working bands are provided in various forms to the subscribers (users).
Two of the above forms in the case of ATM communication services are:
(1) The first is a fixed band (such as the "constant bit rate" (CBR)) service. This service enables a subscriber contracting with this service to always keep a predetermined fixed band width.
(2) The second is a variable band (such as the "unspecified bit rate" (UBR)) service. This service enables a subscriber contracting with this service to provisionally capture a preapplied for fixed band width, however, when the total band width used by all subscribers engaged in communications exceeds the switchable band width in the exchange, maintains communication by not using the excessive band width.
ATM exchanges further come in two types: an independent type where just one of the above fixed band service or variable band service is handled and a common use type where both of these services are handled simultaneously. The present invention relates to mainly the common use type exchange.
2. Description of the Related Art
As will be explained in detail later, assume that, in the above-mentioned common use type exchange, the traffic of some subscribers receiving the variable band service can increase in an instant due to file transfers etc. At this time, the exchange has to secure the contracted fixed band widths for subscribers receiving the fixed band (CBR) service despite the increase in the traffic caused by these subscribers.
This being the case, in order to deal with the instantaneously increased traffic, the exchange has to discard the excess amount of cells from the point of time when the band width exceeds the given band width due to the increased traffic. The discarding of the cells means a deterioration in the quality of transfer of data of the subscribers receiving the variable band service. At this time, a problem arises in fairness if the subscribers, who desire to receive service under the same conditions, are unequally disadvantaged by the deterioration of quality.